From Harvard Business Review:

Overcoming Overthinking

Overthinking can take three forms: rumination, overanalyzing, and future tripping. Here’s how to spot and handle each one—before they cause you to spiral, stress, and ultimately burn out.
 
Rumination. This is a mental loop where you dwell on past events, particularly negative or distressing ones. If you tend to fixate on negative feedback, bring up past failures in conversation with others, or you’re overly cautious about work, you might be a ruminator. To diffuse your rumination, set aside 15 to 30 minutes to grapple with these negative thoughts. This will help you compartmentalize and stop yourself from ruminating constantly throughout the day.
 
Overanalyzing. Procrastinating, over-relying on others’ approval, and experiencing difficulty prioritizing are all tendencies of overanalyzers. To break the cycle, shift your aim from “perfect” to “good enough.”
 
Future tripping. If you spend excessive energy planning for every possible scenario, or you find it hard to celebrate your successes because you’re always thinking about what’s next, you’re likely a future tripper. To address it, use your forward-looking tendencies to your advantage by projecting yourself into a future where the stress of this moment is behind you.